1. Field of the Invention
This invention relates to the art of magnetic recording and more particularly, to magnetic recording media having a specific type of a magnetic thin film on which an information signal is to be recorded. The invention also relates to a method for making such media as mentioned above.
2. Description of the Prior Art
For the high density recording, there are used magnetic recording media comprising a magnetic metal thin film on a non-magnetic substrate. This type of magnetic recording medium should have good magnetic characteristics and particularly a high coercive force. The magnetic metal thin film is usually formed on a non-magnetic substrate by vacuum deposition, in which the stream of a magnetic metal vapor is applied to the substrate at an inclined or oblique angle with respect to the substrate so that a high coercive force is imparted to the resulting magnetic thin film.
In order to obtain, by the oblique deposition technique, a magnetic thin film whose coercive force is as high as possible, the angle of the inclination has to be made as large as possible. However, such a large oblique angle results in an appreciable lowering of film-forming efficiency and thus poor productivity.
Attempts were made to obtain magnetic thin films having a high coercive force by the use of a relatively small incident angle. For instance, there were proposed a method in which such a film was obtained as multi-layered, and a method in which oxygen was introduced during the course of vacuum deposition.
However, the former method is disadvantageous in view of economy because formation of multiple layers undesirably requires a number of complicated steps and a complicated apparatus. On the other hand, the latter method has problems in that the improvement in coercive force by the introduction of oxygen is to an extent of, at most, about 40%; however if the incident angle is small, the coercive force is not improved that much and when the amount of oxygen being introduced is too great, the coercive force is lowered.